A New Asteroseismic $\textit{Kepler}$ Benchmark Constrains the Onset of Weakened Magnetic Braking in Mature Sun-Like Stars

TL;DR

This study introduces a new asteroseismic benchmark star, Papayu, to better understand the transition in magnetic braking efficiency in mature Sun-like stars, supporting the need for weakened spin-down models.

Contribution

The paper presents the discovery and analysis of Papayu, a well-characterized solar-type star, as a new benchmark for testing stellar spin-down models in mature stars.

Findings

Papuya's age and rotation period support weakened spin-down models.

Papuya is at the transition point where traditional and weakened models diverge.

Results reinforce the necessity of revised magnetic braking theories for old stars.

Abstract

Stellar spin down is a critical yet poorly understood component of stellar evolution. In particular, results from the Kepler Mission imply that mature age, solar-type stars have inefficient magnetic braking, resulting in a stalled spin down rate. However, a large number of precise asteroseismic ages are needed for mature ($\geq$ 3Gyr) stars in order to probe the regime where traditional and stalled spin-down models differ. In this paper, we present a new asteroseismic benchmark star for gyrochronology discovered using reprocessed Kepler short cadence data. KIC 11029516 (Papayu) is a bright ($K_{p}$ = 9.6 mag) solar-type star with well-measured rotation period (21.1$\pm$0.8 days) from spot modulation using 4 years of Kepler long cadence data. We combine asteroseismology and spectroscopy to obtain $T_{eff}=5888\pm100$ K, $\rm{[Fe/H]} = 0.30 \pm 0.06\,$ dex, $M = 1.24 \pm 0.05 M_{\odot}$, $R = 1.34 \pm 0.02 R_{\odot}$ and age of 4.0 $\pm$ 0.4 Gyr, making Papayu one of the most similar stars to the Sun in terms of temperature and radius with an asteroseismic age and a rotation period measured from spot modulation. We find that Papayu sits at the transition of where traditional and weakened spin-down models diverge. A comparison with stars of similar zero-age main-sequence temperatures supports previous findings that weakened spin-down models are required to explain the ages and rotation periods of old solar-type stars.